What's the point of hot food?

I'm assuming you're asking why food is often served hot, not why food is often cooked. Cooking can obviously have a major transformation on food. While people often debate whether cold pizza is better than hot pizza, I haven't heard anyone arguing uncooked pizza is the best.

The main reason why foods are often served hot is because higher temperatures increase our perception of taste. However since this increase not uniform across different compounds it can also alter the balance of tastes increasing some more than others, possibly creating a better or worse overall flavour. Temperature can affect how the texture of foods is perceived and even the amount of pain felt when eating spicy hot foods.

Probably the easiest way to test this yourself is would be to compare either soup or coffee served hot as normal and cooled down in a refrigerator. You should notice when served cold the soup has less flavour, and the coffee is noticeably less bitter.

Another thing to try would be beer. It's hard not to notice the difference between an ice cold beer and a room temperature one. While most people prefer their beer as cold as possible, the recommended temperature for craft and specialty beers is often somewhere in the cool range. That's so you actually taste the beer you spent more money on.

Taste can definitely be influenced by temperature. It's easy to experiment. Cook something, eat half of it at the intended temperature, then chill the rest and eat that. Notice the difference. Then repeat that with a dish that doesn't require heating. Eat half of it cold, then heat the rest and eat that. Notice the difference.

Which of these flavours you prefer is probably in part cultural, part personal preference.

If you mean why we started heating our food in the first place, it's largely to do with food hygiene. Cooking meat and plant material kills a lot of the harmful bacteria in it, meaning you're less likely to come down with food poisoning. Freezing has a similar effect, but is far harder to achieve in most climates in a pre-technological society (even in Europe for example, ice was a very expensive luxury in summer until around the 1940s and the advent of electrical freezers. The only ice people had was what was stored in underground ice cellars during winter after being hacked out of rivers and lakes, and slowly melted during the year.

Another reason, one probably discovered by accident in many cases, is that some plants (and probably animals) that are poisonous/toxic before cooking can be safely consumed if heated to a high enough temperature for long enough. This increases the selection of available nutrition, which can be very important for survival as groups grow in size.

By heating or cooking food, you increase the caloric value. Nutrients become available that would otherwise remain locked up.

Sources: https://www.quora.com/Does-warm-food-contain-more-calories-than-cold-ones

Furthermore, if we eat or drink a substance colder than our body core temperature, our body has it to heat it ourselves to 38c/100F. This means cold food will request more calories (or extract heat from your body) than warm food.